The development of safe and effective topical microbicides for the prevention of sexually transmitted diseases is becoming more and more essential in the fight against STD transmission. In this study, we are assessing the anti-chlamydial effects of three newly developed microbicidal compounds, as well as the effects they have on the cervicovaginal environment. With half of the study completed, 30 animals have been evaluated, six in each of five experimental groups. Three groups received microbicidal compounds, one group received a placebo compound, and one group served as a chlamydia control (receiving no pre-inoculation compound). The investigators are blind to the make up of each compound, thereby making definitive results for each microbicide formulation impossible until the end the study. Interim analysis by the funding agency has dictated that the studies continue as planned, until 12 monkeys per experimental group have been evaluated. Animals in the chlamydia control gr oup have all become infected, and none of the experimental groups have shown evidence of deleterious effects to the vaginal flora or to the mucosal tissues of the cervix or vagina. FUNDING NIH grant RR00166 and Conrad Subproject CSA-98-215.